It's the 4th century AD, and one of the greatest civilizations the world had known so far is on the verge of collapse. Rome had split in half and now struggles to maintain its influence, desperately fighting not only barbarian attacks from all sides but also its own internal cultural decline. For the barbarian tribes, it's a bright opportunity to sack a wealthy empire and establish themselves as the next great powers in the region. Meanwhile, the Sassanid Persian empire is in the midst of a golden age, enjoying its imperial glory while fending off its own barbarian assault.
Scenario details
This scenario involves 3 major factions: the Romans, the Sassanids, and the myriad Barbarian kingdoms. It is a score competition that lasts for 70 rounds, with each civilization earning points for controlling an imperial city (either Roman or Sassanid). Each faction is in constant warfare with the others, as such there is no diplomacy, science and religion is outright disabled too.
The Western Roman Empire and Eastern Roman Empire shares their score but manage their respective cities, with Western Rome taking the brunt of barbarian attacks. While they start with the most cities, they will quickly lose this advantage due to the overwhelming force of the other factions without exceptional play. The biggest weakness of the Romans is their social policy tree Roman Atrophy, which inflicts drawbacks with each policy taken. Thus their Culture output becomes cultural decline, and they are forbidden from selling off buildings, forcing them to keep producing Culture in cities. Even worse, each city lost to a barbarian incurs a lump of Culture, so their weakness can quickly snowball out of control.
The barbarian kingdoms comprise of the Celts, the Goths, the Franks, and the Huns. These disparate kingdoms each have their own scores and special traits, but all draw from the same policy branch: Barbarian Zeal, which provides excellent bonuses to military strength and city production.
The Sassanid Empire is a middle ground between the 2 other factions. They start with a fair amount of territory of their own and receive relatively less attention from barbarians. However, their own unique policy tree, Sassanid Legacy, doesn't provide as strong a bonus as the barbarians' branch, which encourages a more steady pace of expansion.